This question concerns freezing point depression and boiling point elevation.

Question

Determine the molality of ethylene glycol in water required to prevent the solution from freezing at -18 degrees C. 

Answer 1

1. To find molality we use the formula ΔT_f = -K_fmi
2. We can rearrange this to find m, So, m = -ΔT_f/K_fi
3. Now plug in our values for what we know to solve for m.
4. m = - (-18ºCº/1.86ºC*kg*mol^-1l*1) --> m = 9.68 mol/kg **1.86 is the K_f of water, and i = 1 because it is v'ant Hoff factor and ethylene glycol does not dissociate into to more than one particle.